Variable-crown rolls comprise a stationary axle inside the roll, on which axle the roll mantle is fitted to revolve. The roll mantle is supported in the press direction on the axle of the roll by means of loading shoes acting upon the inner face of the roll mantle, which shoes are pressed against the inner face of the roll mantle by means of the pressure of a fluid.
In paper machines, rolls which form a dewatering press nip are used commonly. It is important that the distribution of the linear load, i.e. the profile, in the axial direction of the rolls can be made invariable and that the profile can be regulated in the desired way, for example, in view of controlling the cross-direction moisture profile and/or thickness profile of the web. Also in supercalenders, the aim is to be able to regulate the calendering nip in the axial direction of the calender rolls so that the cross-direction thickness profile of the web becomes as desired. For this purpose, from the prior art, a number of different variable-crown or adjustable-crown rolls are known, at which attempts are made to act upon the distribution of the linear load in the nip.
In the rolls mentioned above, it has been noticed that foaming of the fluid is a drawback. The rolls comprise a central stationary axle, in which the loading shoes have been fitted, and the loading shoes project from the axle so that their loading members reach contact with the inner face of the roll mantle. When fluid is sprayed onto the inner face of the roll mantle for the purpose of cooling, or when fluid enters onto the inner face of the roll mantle through lubrication of the loading shoes, the fluid strikes against said loading shoe constructions, in which connection the fluid is atomized and is then readily mixed with air. Great changes in the direction of the fluid cause so-called whipping, which further affects the fluid detrimentally and foams it, in which case the fluid must already be replaced after a short period of use. The operation of the hydraulic components of the system is disturbed and their service life becomes shorter.